Two Visual Mechanisms of Photosensitivity
Article first published online: 2 AUG 2005
Volume 40, Issue 10, pages 1446–1451, October 1999
How to Cite
Harding, G. F. A. and Fylan, F. (1999), Two Visual Mechanisms of Photosensitivity. Epilepsia, 40: 1446–1451. doi: 10.1111/j.1528-1157.1999.tb02018.x
- Issue published online: 2 AUG 2005
- Article first published online: 2 AUG 2005
- Accepted March 10, 1999.
- Photosensitive epilepsy;
- Occipital spikes;
- Photoparoxysmal response
Summary: Purpose: Photosensitive epilepsy is the most common of the “reflex” epilepsies. Precipitated by television viewing, flickering light, or specific visual patterns, it is the cause of seizures in 10% of young people with epilepsy. Photosensitivity is associated with two types of EEG abnormalities: photoparoxysmal responses (PPRs) and occipital spikes (OSs). It is unclear whether these abnormalities are mediated by different mechanisms, and furthermore, the clinical significance of OS is unknown.
Methods: By using our previously established population of patients with photosensitive epilepsy, all showing EEG abnormalities on intermittent photic stimulation or pattern stimulation, we examined the effects of pattern contrast, spatial and counterphase temporal frequency, and colour on these abnormalities.
Results: PPRs and not OSs show linear contrast dependency and are elicited by stationary stimuli and by non-colour-opponent isoluminant stimuli.
Conclusions: PPRs and OSs are generated independently by the parvocellular and magnocellular visual systems, respectively. The results add support to the hypothesis that only PPRs and not OSs are clinically significant.